I first read Cormac McCarthy's Blood Meridian in foul-weather gear, hunched in a corner of the aft stateroom, my legs braced. Outside, the wave tops blown into long streaks of scud. It was my first voyage offshore, I was 29 and the captain. The boat to be my home and business was a 48ft ketch with wooden masts that wallowed and bucked through thousands of miles of ocean. I slept no more than 45 minutes at a time, dreaming always of islands not on the chart rising up beneath our keel. We'd hit, and all hands would be lost. An abstract landscape born of the literal one, "the mountains on the sudden skyline stark and black and livid like a land of some other order out there whose true geology was not stone but fear". This, the extension of the literal landscape, is what McCarthy learned from Faulkner, and this is what I feared when I slept and what I hoped for when I put Blood Meridian down and strapped my laptop to my knees with Velcro. I was writing "Sukkwan Island", the novella at the centre of my story collection Legend of a Suicide, and I was trying to write it through landscape – my native southeast Alaska, rainforest and abandoned islands. I knew I was no Cormac McCarthy, but he is the writer all American writers have to measure themselves against.

Blood Meridian is an anti-western epic, following historical accounts of white scalp-hunters through the American southwest in 1849 and 1850. Its protagonist, "the kid", is not really a protagonist, and we have no access to the thoughts or feelings of any of the characters. The landscape is where we focus instead, and what I like most in the novel is the suggestion of another world inhabited in parallel to ours. A world of metaphor and theme which feels peopled by shadows and imaginings of what we fear and hope for most in ourselves. "Of some other order out there." I'm not religious and I don't like horror, but the demons in Blood Meridian inhabit a shadow world that speaks even to an atheist, an "absolute night" that McCarthy summons from after he has established the landscape "whose true geology was not stone but fear. The thunder moved up from the southwest and lightning lit the desert all about them, blue and barren, great clanging reaches ordered out of the absolute night like some demon kingdom summoned up or changeling land that come the day would leave them neither trace nor smoke nor ruin more than any troubling dream."

I stood on the bow of my boat at night, looking back. Lofting up on each wave, crashing into solid water, vents of spray. The feel of the boat charging forward, three sails curving out to the side. Two red eyes, the forward windows lit in red we used to preserve our night vision, but these did seem like eyes, the boat a kind of dragon. Taiwanese-built, a carving in teak of a dragon on my stateroom door, dragons carved on either side of the bow. I had named the boat Grendel. Standing on that bow, looking back, I was in a desert larger even than McCarthy's and could feel the demon kingdom summoned up. Monsters are supposed to make us whole. Grendel the dark side of man, son of Cain, reuniting with Abel in the form of Beowulf. Is Blood Meridian complete? Is the grappling of the boy and the judge at the end a recurrence of Grendel and Beowulf, or man wrestling directly with God himself, or perhaps with fate, with being? Neither the boy nor the judge descends from Abel, certainly.

I ask these questions because the first time I read the novel, I was lost by the end. I had no idea what to make of the judge or that final grappling with the kid, or the dancing bear or slaughter of the penitents or any of the religious imagery or various burned-out churches along the way. And because I couldn't fit it all together, I wondered whether McCarthy might be flinging us into the void simply for the feeling of the fling itself. I suspected some fakery. And when I reread the novel a year later, to teach it to a class of undergraduates at Stanford, I still couldn't quite put the pieces together. The landscape and vision seemed repetitive, and I wasn't sure it built to more than local effect. But after returning to parts of the book repeatedly over the past 10 years, I do believe that everything fits, and that I understand the vision and the end. Perhaps I'm claiming too much – I really could have much more to learn – but I feel elated by his achievement. Some think Suttree is as great, the inheritance of his earlier works, but for me, only Blood Meridian uses McCarthy's talents fully, and it is specifically because the kid is kept at a distance, the judge is more than mortal, and the landscape and human violence in the landscape come to the fore.

Blood Meridian is the Inferno of our time, though the architecture has changed. Hell here is an open desert landscape, an endless journey past demonic shapes and beings living and dead. "They passed an alkali pan whereon were convoked an assembly of men's heads." Eight heads in a ring facing outward, wearing hats, and the judge kicks one over, reminiscent of Dante kicking a head buried in ice. "They passed lurid and austere the black and desiccated shapes of horses and mules that travellers had stood afoot. These parched beasts had died with their necks stretched in agony in the sand and now upright and blind and lurching askew with scraps of blackened leather hanging from the fretwork of their ribs they leaned with their long mouths howling after the endless tandem suns that passed above them. The riders rode on." Or "a lone tree burning on a desert" circled round by every poisonous thing, and "the strange coral shapes of fulgurite in their scorched furrows fused out of the sand where ball lightning had run upon the ground in the night hissing and stinking of sulphur." There are literally hundreds of these hellish landscapes in Blood Meridian.

Representations of hell have always worked to reveal the shapes of our lives, abstract landscapes meant to describe the felt and suspected landscapes within us. The external world is a sign in fiction, all of it responsive: "Under the hooves of the horses the alabaster sand shaped itself in whorls strangely symmetric like iron filings in a field and these shapes flared and drew back again, resonating upon that harmonic ground and then turning to swirl away over the playa. As if the very sediment of things contained yet some residue of sentience. As if in the transit of those riders were a thing so profoundly terrible as to register even to the uttermost granulation of reality." The landscape in Blood Meridian is a portrait of us, a secular inferno necessary because, although we may not believe, we still know we are doomed. We shall destroy all we know and then live on.

Neither the judge nor the kid is descended from Abel, and their battle has the worst quality of hell, which is that it has no end. The book's main subject, of course, is war, and as the judge tells us by firelight, smeared with animal grease and marrow: "Before man was, war waited for him. The ultimate trade awaiting its ultimate practitioner. That is the way it was and will be. That way and not some other way." This is the most important chapter of the book, chapter 17, when the judge holds forth on order and teleology and war. The landscape that follows his discussion is specifically compared to hell and is perhaps the most hellish yet: "they crossed the malpais afoot, leading the horses upon a lakebed of lava all cracked and reddish black like a pan of dried blood, threading those badlands of dark amber glass like the remnants of some dim legion scrabbling up out of a land accursed . . . a cinderland of caked slurry and volcanic ash imponderable as the burnedout floor of hell." Teleology is the study of an end, and McCarthy is more interested in this than he is in the study of origins. The kid and the judge in their grappling are "a forcing of the unity of existence". They are war, continual war, and "war is god". Grendel and Beowulf without redemption. That's the future McCarthy sees for us.

In the final pages, the judge proclaims himself the devil: he never sleeps and will never die. There is rumour of him everywhere among "the cries of the lost" at "the fire in the lake". He is without origins: "nor was there system by which to divide him back into his origins for he would not go", "no trace of any ultimate atavistic egg by which to reckon his commencing". But the kid is no innocent: on the opening page of the novel, "in him broods already a taste for mindless violence". On the second page, a kind of thesis for the kid: "His origins are become remote as is his destiny and not again in all the world's turning will there be terrains so wild and barbarous to try whether the stuff of creation may be shaped to man's will or whether his own heart is not another kind of clay." The kid is a test of all of us, and the judge would have us believe in predestination, but I don't believe him. He fabricates a sense of order for his own entertainment only. Beside him, a "coldforger . . . contriving from cold slag brute in the crucible a face that will pass, an image that will render this residual specie current in the markets where men barter." This is McCarthy, I think. He is the artisan at work here, contemplating the limits of his own achievement. He is hammering out "some coinage for a dawn that would not be".

A great American novel can only be anti-American, and Blood Meridian, like Toni Morrison's Beloved, focuses on our greatest shames, in this case our genocides and our desire for war, contemplating in its final chapters the slaughter of the buffalo; also the slaughter of innocence in the form of a dancing bear, and the slaughter of any would-be penitents, including the kid. The last look west has to see nowhere else to go.